Febrile seizures are generalized convulsions that occur during a fever. Most febrile seizures occur between the ages of 6 months and 4 years. Febrile seizure is the most common cause of seizure in children, with up to 5% of all children having at least one febrile seizure by age 5 years. There is a strong genetic predisposition (first-degree relatives have up to three times greater risk of febrile seizure than the general population).187 Approximately one-third of children who have a febrile seizure have another seizure during a subsequent febrile illness, but only 2% of children whose first seizure is associated with fever will develop true epilepsy.187
The challenge to clinicians is to distinguish febrile seizures, which are frequent and benign, from seizures of identical phenomenology with potentially deadly origins, including infection, that require acute intervention, A single, brief generalized seizure occurring concurrently with fever is likely to be a simple febrile seizure.187 Complex febrile seizures can also occur; they frequently have focal features, last longer than 15 minutes, and recur within 24 hours.187
Children with simple febrile seizures are usually normal postictally. In contrast, 90% of seizures secondary to meningitis are followed by postictal stupor, and most of the remaining 10% demonstrate other meningitic signs, such as nuchal rigidity.187
Because up to 30% of children with bacterial meningitis have a seizure, it is frequently taught that lumbar puncture (LP) is mandatory for children who have fever and seizure, because the convulsion may be the sole manifestation of bacterial meningitis. Data suggest, however, that this principle is excessively invasive. Green and colleagues reviewed over 500 consecutive cases of meningitis in children aged 2 months to 15 years. They found that meningitis was associated with seizures in 23% of cases, but all of these patients presented with signs in addition to the fever and seizure. Over 90% presented with significant sensorium change, and the others presented with nuchal rigidity or other straightforward indications for LP. No patients were found to have bacterial meningitis manifesting solely as a simple seizure. The authors concluded that commonly taught rules requiring LP in children with fever and seizure are unnecessarily restrictive.188
A retrospective study of pediatric patients presenting to the emergency room for evaluation of febrile seizures was performed to determine the incidence of bacteremia, urinary tract infections, and unsuspected bacterial meningitis. (Children with known seizure disorders, chronic neurologic disease, documented immunodeficiencies, or initial laboratory evidence of meningoencephalitis in the emergency room [more than 8 WBC in CSF] were excluded).189 Blood cultures were performed on approximately 85% of patients. Of these, 2.9% were positive, all for Streptococcus pneumoniae. Urine cultures were performed in just over half of cases, and only 0.7% of these yielded a bacterial pathogen. CSF cultures were performed in 27% of encounters and none yielded bacterial pathogens. The investigators concluded that children presenting for evaluation of febrile seizures are not at increased risk for bacteremia or urinary tract infection. Furthermore, in the absence of initial lab evidence of meningoencephalitis, bacterial meningitis is very uncommon in children diagnosed with febrile seizures.189
Al-Eissa prospectively studied LPs performed in children with fever and seizure to identify the criteria used by emergency physicians in selecting patients for LP. Of 200 previously healthy children aged 3 months to 5 years brought to a pediatric emergency room with fever and seizure, LP was performed in 51% of cases and resulted in detection of seven (3.5%) cases of meningitis, three (1.5%) of which were bacterial. Seizures with complex partial features had significant influence on the decision to perform an LP.190
To determine whether complicated febrile seizures occur more often in children with viral infection, especially HHV-6, Rantala and colleagues studied 144 children with febrile convulsions, of whom 112 had simple and 32 had complex partial seizures. A diagnosis of virus infection was verified in 46% of simple partial seizure cases and 53% of complex partial seizures. In a follow-up of 2 to 4 years, children with positive evidence for a viral infection (even with virus isolated from CSF) had no more recurrences than those without any proven viral infection. The investigators concluded that children with febrile convulsions who have proven viral infection have no worse prognosis than those without.191
Reviewed and revised March 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.
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